This invention relates to high voltage electrical switchgear.
For safety considerations, an open circuit is visually verified before work is performed on a high voltage power distribution system. An open circuit may be created by high voltage load interrupters (switches) that use oil or vacuum as the interrupting medium. Vacuum switches have extremely long lifetimes and are resistant to degradation caused by electrical arcing. However, the contacts of a vacuum switch are contained in a sealed ceramic bottle and the on/off state of the vacuum switch cannot be visually verified.
Visual verification may be provided using oil switches. Oil switches are often designed and placed near a window in an oil filled tank to provide the required visual open circuit. Nevertheless, oil switches may sustain damage if used to switch load currents. For example, electrical arcing in an oil switch may seriously degrade the oil switch by reducing the insulative properties of the oil, as well as by creating explosive gases. Also, electrical arcing may carbonize the oil, which may cause it to become opaque over time and defeat the ability to visually verify an open circuit.
In one general aspect, an interlock mechanism ensures that a first switch does not switch to a first position unless a second switch is in a second position and that the second switch does not switch from the second position while the first switch is in the first position. The interlock mechanism includes a moveable body with a notch configured to associate a position of the moveable body with a switching of the second switch. The associated position of the moveable body locates the notch in an engagement position when the switch is in the second position and locates the notch out of the engagement position when the switch is not in the second position. The interlock mechanism also includes a rod structured and arranged to engage the notch of the moveable body when the first switch is in the first position and to disengage the notch of the moveable body when the first switch is switched from the first position. When the rod engages the notch of the moveable body, the rod blocks movement of the moveable body in a first direction and prevents the second switch from switching from the second position. When the notch of the moveable body is not in the engagement position, the rod may not engage the notch and the first switch is prevented from switching to the first position.
Implementations may include one or more of the following features. For example, the first switch may include a primary vacuum switch, and the first position of the first switch may correspond to a closed position of the primary vacuum switch. The second switch may include, for example, a secondary safety switch (e.g., an oil immersed switch), and the second position of the second switch may correspond to a closed position of the secondary safety switch. Both the primary vacuum switch and the secondary safety switch may be switchable between an open position and a closed position.
A high voltage switchgear may exhibit both the long operational life of a vacuum switch and the visual verification of an oil switch by incorporating the interlock mechanism in conjunction with an oil switch in series with a vacuum switch. In a high voltage switchgear so configured, the vacuum switch performs the primary switching function, while the oil switch performs a secondary switching function. The interlock mechanisms ensures that the vacuum switch is switched under load conditions and the oil switch is switched after the load has been removed by the vacuum switch or before the load is restored by the vacuum switch. The ability to view the on/off status of the contacts of the oil switch is preserved by using the interlock mechanism to prevent arcing when the oil switch is switched.
In one implementation, the moveable body of the interlock mechanism may include a rotatable cylinder or an annular cam connected to a rotatable shaft. In either case, the notch may include an approximately radial notch into the rotatable cylinder or the annular cam. The notch in the cylinder or the annular cam may be structured and arranged to present approximately a right angle to the rod. The rod may include a rod rotatably attached to a pivot point at a first end and structured and arranged to rotate into or out of the notch when the notch is in an engagement position.
In another implementation, the moveable body includes a planar body structured and arranged to move longitudinally. The planar body may include a first planar surface that is oriented toward the rod, and the first planar surface may include the notch. There also may be a second surface of the planar body that includes drive teeth. The drive teeth may engage a drive gear sprocket to induce longitudinal motion of the planar body.
The notch in the planar body may include an indentation in the first planar surface of the planar body, with the indentation being structured and arranged to engage the rod. The notch also may include a cut-through in the first surface of the planar body that extends through a thickness of the planar body and that is structured and arranged to engage the rod. The rod may be structured and arranged to move essentially perpendicularly to the planar body and into and out of the notch when the notch is in an engagement position.
In yet another variation, the planar body includes a longitudinal slot in the first planar surface of the planar body. The slot is structured and configured to receive the rod, and includes a section of the slot with a lateral notch structured and arranged to engage the rod. The rod may be structured and arranged to move laterally with respect to a longitudinal direction of motion of the planar body and the slot. This may allow the rod to move into and out of the notch when the notch is in the engagement position.
A first switching mechanism may be structured and arranged to switch the first switch, and a linkage mechanism may be provided to link the movement of the rod to the operation of the first switch. A second switching mechanism may be structured and arranged to switch, the second switch and a linkage mechanism may be provided to link the movement of the moveable body to the operation of the second switch, such as, for example a stub shaft of the second switch.